Javier Duarte kicked off his scientific career by witnessing the biggest particle physics event in decades.Duarte was an eager graduate student who’d just arrived at CERN.
“I was physically there maybe a week before the announcement,” Duarte says. As buzzing throngs of physicists crowded together to watch the announcement at CERN, Duarte didn’t make it to the main auditorium. That space was for VIPs — and those determined enough to wait in line all night to snag a seat. Instead, he says, he found himself in the basement, in an overflow room of an overflow room.
But the enthusiasm was still palpable. “It was a very exciting time to be getting immersed into that world,” he says. Since then, he and thousands of other physicists from around the world working on CERN experiments have gone all out exploring the particle’s properties.
Scientists predicted the existence of the Higgs boson back in 1964, as a hallmark of the process that gives elementary particles mass. But finding the particle had to wait for CERN’s Large Hadron Collider, or LHC. In 2010, the LHC began smashing protons together at extremely high energies, while two large experiments, ATLAS and CMS, used massive detectors to look through the debris.
The particle’s discovery filled in the missing keystone of the standard model of particle physics. That theory explains the known elementary particles and their interactions. Those particles and interactions are behind just about everything we know. The particles serve as building blocks of atoms and transmit crucial forces of nature, such as electromagnetism. And the mass of those particles is key to their behavior. If electrons were massless, for example, atoms wouldn’t form. Without the Higgs boson, then, one of scientists’ most successful theories would collapse.
The Higgs boson discovery dominated headlines around the globe. About half a million people tuned in to watch the livestreamed announcement, and footage from the event appeared on more than 5,000 news programs. Even oddball minutiae made it into the press, with a few articles analyzing the physicists’ use of the often-scorned font Comic Sans in their presentation. Little more than a year later, the discovery garnered a Nobel Prize for two of the scientists who developed the theory behind the Higgs boson, François Eng let and Peter Higgs — for whom the particle is named.
Now, as the discovery turns 10 years old, that initial excitement persists for Duarte and many other particle physicists. As a professor at the University of California, San Diego and member of the CMS experiment, Duarte’s research still revolves around the all-important particle. Progress in understanding the Higgs has been “stunning,” he says. “We’ve come so much farther than we expected to.”
Physicists have been working through a checklist of things they want to know about the Higgs boson. They spent the last decade cataloging its properties, including how it interacts with several other particles. Though measurements have so far been in line with the predictions made by the standard model, if a discrepancy turns up in the future, it may mean there are unknown particles yet to be discovered.
And there’s still more on the agenda. An especially important item is the Higgs boson’s interaction with itself. To help pin down this and other Higgs properties, scientists are looking forward to collecting more data. Scientists turned to an upgraded LHC for a new round of work in April. At the time of the Higgs discovery, collisions at the LHC reached an energy of 8 trillion electron volts. Collisions are expected to roll in at a record 13.6 trillion electron volts starting July 5, and data-taking will continue until 2026. These higher energies offer opportunities to spot heavier particles. And the High-Luminosity LHC, a more powerful iteration of the LHC, is expected to start up in 2029.
“Finding a particle, it sounds like the end of something, but it’s really only the beginning,” says experimental particle physicist María Ceded of CIE MAT in Madrid, a member of the CMS collaboration.
COUPLING UP
Studying the Higgs boson is like geocaching, says theoretical particle physicist Gudrun Heinrich of the Karlsruhe Institute of Technology in Germany. Much like hobbyists use a GPS device to uncover a hidden stash of fun trinkets, physicists are using their wits to uncover the treasure trove of the Higgs boson. In 2012, scientists merely located the cache; the next 10 years were devoted to revealing its contents. And that investigation continues. “The hope is that the contents will contain something like a map that is guiding us towards an even bigger treasure,” Heinrich says.
B Detailed study of the Higgs boson could help scientists solve mysteries that the standard model fails to explain. “We know that the theory has limitations,” says theoretical particle physicist Laura Reina of Florida State University in Tallahassee. For instance, the standard model has no explanation for dark matter, a shadowy substance that throws its weight around the cosmos, exerting a gravitational pull necessary to explain a variety of astronomical observations. And the theory can’t explain other quandaries, like why the universe is composed mostly of matter rather than its alter ego, antimatter. Many proposed solutions to the standard model’s shortcomings require new particles that would alter how the Higgs interacts with known particles.
The Higgs boson itself isn’t responsible for mass. Instead, that’s the job of the Higgs field. According to quantum physics, all particles are actually blips in invisible fields, like ripples atop a pond. Higg's bosons are swells in the Higgs field, which pervades the entire cosmos. When elementary particles interact with the Higgs field, they gain mass. The more massive the particle, the more strongly it interacts with the Higgs field, and with the Higgs boson. Massless particles, like photons, don’t directly interact with the Higgs field at all.
One of the best ways to hunt for Higgs-related treasure is to measure those interactions, known as “couplings.” The Higgs couplings describe what particles the Higgs boson decays into, what particles can fuse to produce Higgs bosons, and how often those processes occur. Scientists gauge these couplings by sifting through and analyzing the showers of particles produced when Higgs bosons pop up in the debris of proton smashups.
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